Radial piston hydraulic device

ABSTRACT

A radial piston-type hydraulic motor has a rotatable inner body element journaled in a fixed housing having a plurality of rollers disposed at equiangular intervals about the axes of the inner body element and axially parallel thereto. The inner body element has a plurality of radially extending cylinders with reciprocating pistons disposed around the inner body element at equiangular intervals preferably greater than the angular intervals between the rollers. The outer end of each piston is provided with a cam engageable with the rollers to cause rotation of the inner body element in response to reciprocation of the pistons.

United States Patent Kress RADIAL PISTON HYDRAULIC DEVHCE Primary Examiner-Paul E. Maslousky Attorney-H. Vincent Harsha, Harold M. Knoth, Wil- [72] Inventor: a Henry Kress Cedar Falls liam A. Murray, John M. Nolan and Raymond L. Hollis'ter [73] Assignee: Deere & Company, Moline, Ill.

[2H Appl 65381 A radial piston-type hydraulic motor has a rotatable inner body element journaled in a fixed housing hav- [52] 0.8. CI ..9l/492, 91/180 ing a plurality of rollers disposed at equiangular inter- [51] Int. Cl, ,F01b 1/06, F01! 13/06, F01] 33/02 vals about the axes of the inner body element and axi- [58] Field of Search .91/180, 492, 491, 497,496, a ly pa all l th to- Th inn r b dy element has a 91/498 plurality of radially extending cylinders with reciprocating pistons disposed around the inner body [56] References Cited element at equiangular intervals preferably greater than the angular intervals between the rollers. The UNITED STATES PATENTS outer end of each piston is provided with a cam en- 3 593 621 7/1971 Praddaude .L ..91/498 gageahle With the toilets to cause rotation of the inner 3:081:708 3/1963 Nyman et al. ..91/492 body element in response to reciprocation of the 3,165,029 1/1965 Haldiman ..91/180 plstohs- 3,511,131 5/1970 Kress ..9l/180 FOREIGN PATENTS OR APPLICATIONS 4 Claims, 2 Drawing Figures 976,857 11/1950 France ..91/498 r 4s 48 22 4 e2 11 E33? jl 66 1" Ki I 1210 14 568 28 56 72 7 :1 42 L93} 64 l L 24 1 1 3s 34 38 RADIAL PISTON HYDRAULIC DEVICE BACKGROUND or THE INVENTION This invention relates to a radial piston-type rotary hydraulic machine, and more particularly to a hightorque, low-speed hydraulic motor of the type having a relatively large number of radial pistons wherein the motor rotates in response to reciprocation of the pistons through a camming action between the pistons and the housing, each piston going through a relatively large number of cycles for each, revolution of the motor, to give the motor its high-torque, low-speed characteristic.

Such hydraulic motors, sometimes referred to cam lobe motors, are relatively new, and have been used recently in some low-speed, high-torque applications, such aswheel motors for hydraulically driven vehicles. In such an application, the motors have the advantage of not requiring reduction gearing between the output of the motor and the wheel.

Heretofore, such motors have conventionally utilized a generally sinusoidal cam ring having a different numberof cam lobes than the number of pistons, each piston conventionally being provided with a roller ,engageable with the cam surface to reduce the friction between the piston and the cam Such a motor is shown in the applicants recently issued U. S. Pat. No. 3,51 1,131.

SUMMARY OF THE INVENTION According to; the present invention, there is provided an improved design for a rotary radial piston hydraulic device, such as shown in U. S. Pat. No. 3,51 1,131. More specifically, the radial pistons are provided with cams at their exterior ends, which engage rollers journaled in the motor housing outwardly of the pistons. This arrangement eliminates the relatively expensive, multi-lobed cam ring, reducing both the cost and the size of the motor. It also provides a lower inertia piston as compared to previous motors of this type, allowing higher speeds and reducing inertia forces.

Another feature of the invention resides in the arrangement of the radial pistons with the pistons staggered in two axially spaced banks, whereby the cams on the end of each piston span the are between adjacent rollers to provide a smooth transition of the piston between the rollers. I

Still another feature ofthe invention resides in the fact that the cam surfaces at the point of contact with the rollers during the transition period are perpendicular with the radial line drawn between the moto'rs axis and the axis of the rollers so that the pistons have a zero radial velocity at the transition period.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial section through the hydraulic motor, as viewed generally along the line l--! of FIG. 2.

FIG. 2 is an enlarged section of the motor only, as viewed generally along line 2-2 of FIG. 1, and with a portion of the inner. body or hub of the motor broken away to show the second bank of pistons.

DESCRIPTION OF THE PREFERRED EMBODIMENT The rotary radial piston-type fluid energy translating device is illustrated as a hydraulic wheel motor, for a tractor or the like, similar to the wheel motor shown in said U. S. Pat. No. 3,51 1,131. The axle structure, which forms the environment for the motor, is indicated generally by the numeral 10, and, as is conventional, has a yoke 12 at its outer end with vertically separated arms, which respectively carry vertically aligned top and bottom pivot pins 14 and 16, respectively. A hydraulic wheel motor, indicated generally by the numeral 18, is mounted for steering articulation on the pivot pins, and includes a motor housing or outer body element 20 having upper and lower axially aligned bearings 22 and 24, respectively, which receive the pivot pins 14 and 16 to permit the housing to swing about the vertical axis of the pivot pins 14 and 16. An axial shaft 26 is joumaled in the housing 20 in inner and outer bearings 28 and 30, respectively, the outer end of the shaft projecting through the housing and being attached to a conventional wheel structure, indicated in its entirety by the numeral 32.

The housing 20 is generally cylindrical and has a generally cylindrical inner cavity 34 coaxial with the shaft 26. A plurality of rollers 36 are mounted within the cavity 34 axially parallel to the shaft 26 and have their opposite ends joumaled in the housing via bearings 38. The rollers 36 traverse the'cavity 34 and are spaced at equiangular intervals about and equidistant from the axis of the motor shaft 26. In the illustrated embodiment, 14 rollers are provided so that the angular spacing between adjacent rollers is approximately 25.7.

The hydraulic motor also includes a generally annular hub or inner body element 40 coaxially splined to the shaft 26 within the cavity 34. The hub or inner body element 40 has a plurality of radially extending, outwardly open cylinders 42, with a piston 44 mounted for reciprocation within each cylinder. The cylinders are also spaced at equiangular intervals about the axis of the motor shaft 26, and are staggered in two axially spaced banks. In the illustratedembodiment, 12 cylinders are provided with six cylinders in each bank, so that the cylinders in each bank are spaced at 60 intervals and offset 30 from the cylinders in the other bank, whereby the 12 cylinders are disposed at 30 intervals about the shaft axis, as best seen in FIG. 2. When viewed in FIG. 2, the cylinders in the 12, 2, 4, 6, 8, and 10 o'clock positions are in the outer bank (the lefthand bank in FIG. 1) while the 1,3,5, 7, 9, and 11 oclock cylinders are in the inner bank.

While 12 pistons and 14 rollers are shown in the illustrated embodiment, it is to be understood that different quantities of both can be used, the numbers being selected to meet size and cost objectives and to obtain a smooth torque. The number of pistons is preferably less than the number of rollers to produce less scuffing between the rollers and pistons.

The outer end of each piston 44 is provided with a hat-like cam 46 exteriorly of the hub or inner body element 40. Each cam has a generally sinusoidal cam surface 48, generated by a series of lines parallel to the axis of the shaft26 and rollers 36. Each cam surface 48 has a central peak 50 at the center of the piston, and

has symmetrical surfaces on both sides of the central peak 50. The total angular width of the cam surfaces relative to the axis of the motor is slightly greater than the 25.7 spacing between adjacent rollers, as can best be seen in FIG. 2 wherein the opposite ends of the cam surface on the 9 oclock piston extends slightly beyond the radius lines 52 on which the adjacent rollers 36 are mounted As is apparent, the 9 oclock piston is centered between the two adjacent rollers and is in a transition phase wherein its cam surface engages both rollers. As is also apparent, when the pistons are at their transition point, the cams engage the rollers approximately at the radius lines, and the cam surface at the point of engagement is approximately perpendicular with the radial line, sothat during the transition between rollers there is no torque transmitted between the cam surface and the rollers.

The pistons are biased outwardly against the rollers by a piston spring 54 acting between the piston and the inner or closed end of each cylinder. The closed end or inner end of each cylinder communicates with an axially extending passage 56 between each cylinder and the inner radial face of the hub 40.

Fluid under pressure is supplied to and exhausted from the wheel motor 18 through a pair of hydraulic lines 58 and 60, respectively, extending through the upper and lower pins 14 andl6. The lines 58 and 60 are respectively connected to fluid passages 62 and 64 in the motor housing 20. Mounted within the housing 20 is an annular manifold 66, which coaxially surrounds the shaft 26 and has a first series of passages 68 communicating with the passage 62, and a second series of passages 70 connected to the passage 64. The passages 68 and 70 extend to the outer radial face of the manifold 66, and an annular valve plate 72 is doweled to and rotatablewith the hub 40 and is interposed between the inner radial face of the hub and the outer radial face of the manifold 66. The valve plate has a series of axially extending passages 74 connected to the passages 56, and as the valve plate rotates relative to the manifold 66, the passages 74 and consequently the passages 56 and cylinders 72 are alternately connected to the manifold passages 68 and 70, so that fluid pressure is alternately supplied to and exhausted from the cylinders as the hub 40 and valve plate 72 rotate. The relationship between the manifold and the valve plate is described in greater detail in U. S. Pat. No. 3,51 1,131.

During forward operation of the wheel motor, fluid pressure is supplied through the hydraulic line 58 and the line 60 is connected to the reservoir. When the motor is in the position shown in FIG. 2, pressurized fluid is applied to the cylinders shown in the 4, 5, l0, and ll o'clock positions, fluid is being exhausted from the cylinders in the l, 2, 7, and 8 oclock positions, and the cylinders in the 3, 6, 9, and 12 o'clock positions are in their transition phase wherein they are disconnected from both the inlet and outlet, the l2 oclock and 6 oclock pistons being at their minimum extension and the are such that the outward movement of the pistons exerts a torque which rotates the hub 40 and confiiiilii fi uiiihfi kfvii ii flcf zil Wu???" times there are at least four pistons in their power stroke, with the opposite pistons being in the same stage of their stroke, so that balanced forces are applied to the rotating hub 40. Since each piston goes through one cycle as it moves from one roller to the next, each piston 44 reciprocates 14 times for each revolution of the hub 40 and shaft 26, giving the motor its high-torque, low-speed characteristic.

As is apparent, the staggered arrangement of the pistons permits each piston to have a cam surface wider than the included angle between adjacent rollers without interfering with the next piston, and the relatively wide cam surface permits a smooth transition from one roller to the next. The design of the cams 48 is such that a relatively constant torque is exerted by the motor during its operation. By supplying the pressurized fluid to the hydraulic line rather than the line 58, the power stroke of each piston will occur on the opposite side of each roller from that previously described, so that the torque exerted on the hub is opposite that described above, to rotate the wheel in the reverse direction.

lclaim:

l. A fluid energy translating device comprising: An outer body element having an internal cavity; an inner body element joumaledwithin the outer body element cavity and forming an annular chamber; a plurality of radially extending outwardly open cylinders disposed at equiangular intervals in said inner body element; a piston mounted for reciprocating movement in each cylinder; a cam mounted on the outer end of each piston and having an outwardly facing sinusoidal cam surface disposed in theannular chamber with the peak of the cam surface disposed on the axis of the piston; a plurality of rollers journaled in the outer body element and disposed in the annular chamber axially parallel to the inner body element and engageable with the cam surfaces during rotation of the inner body member; and valve means for controlling the flow of fluid to and from the cylinders.

2. The invention defined in claim 1 wherein the valve means directs fluid pressure to certain of said cylinders to force the pistons therein outwardly so that the cam surfaces on said pistons engage the rollers to exert a torque on the inner body element, the valve means exhausting fluid from the cylinder of the pistons being forced inwardly by the engagement of their cam surfaces with the rollers.

3. The' invention defined in claim 2 wherein the rollers are equiangularly spaced about the axis of rotation and the cylinders are also equiangularly spaced about said axis, but at a greater angular spacing than the rollers.

4. The invention defined in claim 1 wherein each cam surface has a peak at the axis of the associated 3 o-clock and 9 o'clock pistons being at their maximum 60 piston and sinusoidal inwardly inclined surfaces on extension. As is apparent, the pressurized fluid forces the respective pistons outwardly, and the cam surfaces both sides of the peak parallel to the axis of rotation.

i 4! l i 

1. A fluid energy translating device comprising: An outer body element having an internal cavity; an inner body element journaled within the outer body element cavity and forming an annular chamber; a plurality of radially extending outwardly open cylinders disposed at equiangular intervals in said inner body element; a piston mounted for reciprocating movement in each cylinder; a cam mounted on the outer end of each piston and having an outwardly facing sinusoidal cam surface disposed in the annular chamber with the peak of the cam surface disposed on the axis of the piston; a plurality of rollers journaled in the outer body element and disposed in the annular chamber axially parallel to the inner body element and engageable with the cam surfaces during rotation of the inner body member; and valve means for controlling the flow of fluid to and from the cylinders.
 2. The invention defined in claim 1 wherein the valve means directs fluid pressure to certain of said cylinders to force the pistons therein outwardly so that the cam surfaces on said pistons engage the rollers to exert a torque on the inner body element, the valve means exhausting fluid from the cylinder of the pistons being forced inwardly by the engagement of their cam surfaces with the rollers.
 3. The invention defined in claim 2 wherein the rollers are equiangularly spaced about the axis of rotation and the cylinders are also equiangularly spaced about said axis, but at a greater angular spacing than the rollers.
 4. The invention defined in claim 1 wherein each cam surface has a peak at the axis of the associated piston and sinusoidal inwardly inclined surfaces on both sides of the peak parallel to the axis of rotation. 